The present invention relates generally to the production of laminated paper products and, more particularly, to an apparatus for laminating a continuous web of plastic film material to a continuous web of paper backing material which includes a system for controlling the relative width change of the plastic film web during a plastic film web length adjusting operation performed immediately prior to lamination of the plastic film web to the paper web.
Lamination of a plastic film material to a paper material has been found to be particularly advantageous where paper products having high strength and abrasion resistant qualities are required. Such laminated composites are particularly desirable in the packaging industry, where artwork may be printed on the interior side of the plastic film to produce a high quality display package. The construction and use of such laminated composites are described in Peer, U.S. Pat. Nos. 4,254,173; Haake et al, 4,496,417; Jensen et al., 4,572,752; Jensen, 4,610,739; and U.S. patent application Ser. No. 835,234 of Thompson et al., filed Mar. 3, 1986, which are hereby incorporated by reference for all that is disclosed therein.
In producing a laminated composite of the type described in Peer, both the plastic film material and the paper material may be provided in continuous sheets from spools. The paper and the plastic film generally pass over a number of roller-type devices where each of the materials are independently stretched out under tension and treated as necessary depending upon the particular end use for the laminated composite. For example, the plastic material may be irradiated in conventional processes to increase its strength or improve its printability. The plastic may be printed with various graphics and provided with a metalized background over the graphics to enhance the package appearance. The paper web and film web may be oppositely electrostatically charged to aid in the bonding process. Either the film material or the paper material or both are treated thereafter with suitable adhesive to provide a bond between the paper and film. To complete the laminating process, the paper and film material are pressed together between opposed rollers to produce a smooth, flat composite. Various heating or cooling processes may also be required to ensure proper adhesion of the surfaces, depending on the type of the film, paper, and adhesive agent which are being used in the laminating process. The end product of the laminating process is a laminated composite which may be fed directly to cutting dies or other machines for further processing. The composite may also be taken up directly on a separate spool for storage and later processing.
Use of a film/paper composite provides many advantages over conventional packaging material but also creates some unique problems. In order to be cost-effective, the plastic film material used is generally quite thin, on the order of 0.25-2.0 mils. Plastic films of such thicknesses tend to stretch or shrink during the lamination process: probably as a result of variations in the strength of the film caused by temperature variations and as a result of the different inertial forces exerted on the film as it is unrolled and processed prior to bonding with the paper, and as a result of other forces and effects. Such stretching and shrinking may cause warping or buckling in the laminated composite as the film returns to a steady state condition after lamination. In many cases, a repeating image is printed on the film for later lamination in registry with predetermined lengths of paper material. In such cases, the printed image length must be held within close tolerances in order to permit proper registry with other processing activities such as automated cutting in a later process step. Stretching or shrinking of the film web effects such length registry.
Apparatus for controlling the length distortion of an extensible plastic film web used in a film/paper laminate are disclosed in the above referenced patents of Haake et al. and Jensen et al., and in the patent application of Thompson et al.
However, in length adjusting operations such as described in the above patents and patent application, an attendant problem of width fluctuation has been experienced. Longitudinal tension variation through relative nip speed control which is used to obtain proper length adjustment in repeat length portions of a film web has been found to produce non-uniform variations in web width. Thus, even though such apparatus may hold the length of repeat length portions of a film web at a substantially constant value at the laminating station, the width of the web at the laminating station has been found to vary. As a result, the laminated composite and the carton blanks, etc., formed from the laminated composite have been somewhat non-uniform in a dimension thereof corresponding to the lateral (width) dimension of the film web. On approach for solving this problem is described in Jensen, U.S. Pat. No. 4,610,739, which is hereby incorporated by reference for all that is disclosed therein. In that patent, a width control method comprising monitoring of the film width; engaging opposite lateral edges of the film web between gripping belt assemblies; and pivoting the belt assemblies outwardly or inwardly in response to a width monitoring signal to provide relative stretching or shrinking in the lateral dimension of the film web is disclosed.
Applicants have discovered that the relative width of a moving plastic film web undergoing length adjustment, such as described in U.S. Pat. Nos. 4,496,417 and 4,572,752, may be controlled by controlling the temperature of the plastic film web during the length adjusting operations. It is applicant's theory that temperature effects the ratio between the change in thickness and the change in width that a film web undergoes during a change in length of the type described in U.S. Pat. Nos. 4,496,417 and 4,572,752.